Process for detanning.



scams.

" NITE STATES PATENT OFFICE.

ALBEBTG. mus, OE OCONOMOWOC, WISCONSIN, ASSIGNOB 'lO ALBERT O. TBOSIEL,

' OF .MILWAUKEE, WISCONSI N.

raocnss For. nnrnmme.

1T0 Drawing.

1o aliy to' a process for detanning chrome tanned leather or leatherwaste, etc. I

The salient objectof the invention is to provide a process wherebychrome tanned eathcr or leather waste may be thoroughly detanned withoutimpairing, or substantia-lly impairing, its strength or structure, sothat upon the completion of this detanning process it will be restoredpractically to its original untanned con'dition and the product maythereafter be utilized for any of the numerous uses to which untannedhides or scrapsfof hides might be converted.

Other objects of the invention are to provide. a process which is simle, economlcal,

and by means of which the c emical used in tanning the leather may berecovered-as abyproduct; to provide a rocess which is admirabliy. suitedfor p acing the material treate rovi e a process which is especiallyappllcable for treating finely comminuted 'wasteleather without loss orwaste of the material; to provide a process which may be carried throughin a comparatively short time, and

in general to provide an improved process 7 of thecharacter referred VIn the manufacture and working up of chrome tanned leather there is acompara- 4.o .tively large percentage of so-called waste,

whichhas heretofore been of little or no value because of. the lack ofany suitable process for utilizing such waste. Such waste includesso-called' skivings, splits,

'45 trimmings, skiflings, shavings, their pieces torn off in shaving forother working-of skins, and inferior and rejected. pieces of lathenMoreover, in making chrome 'tanned leather for grain finish thereusually results a certain proportion of hides 'which turn out to be'unsat1sfactory for this kind of leathery-the defective character of ythe hides being onl determinable by tanningthem, and these 'des. can beadvantageously detanned by my process and then retanned Specification ofLetters Patent.

inlcondition for making either ood 30 gelatin orhigh grade glue; to -pPatented Au 16, 1910.

Application filed April 5, 1909. Serial No. @8305.

by some other rocess, as for example to produce a flesh hed leather.Where the waste is in the form of scraps or F shavings, unsuitable foruse as leather, the detanned product secured by my process may beconverted into gelatin, lueor even into animal food, since the, productis, as above stated, returned substantially to its original animalcondition. p

, The preferred way of carrying out my process is as follows: I firstsubject leather or leather waste to a bath or treatment of hot water,which rapidly softens the material and puts it in condition for thesubsequent chemical treatment to affect it rapidly and uniformly. Thehot water treatment is continued until the material is all thoroughlypenetrated and softened. I

alkaline solution, which has the effect of next treat the material in abath of a weak loosening the'chrome so that it will readily andthoroughly dissolve in the subsequent acid treatment. For this chemicalbath I prefer to use lime water,-not milk of lime, because the useof'the latter results in mix ing the mineral lime into the finelycom-Imnuted and powdered waste to such an extent that a substantialpercentage of it is inevitably lost in the subsequent washing out of thelime, besides makin it more di'flicult toseparate the alkali and huefrom the material being treated. Ordinarily the lime water treatmentwill cover a period of from six totwelve hours. I next remove. the limewater and preferably also wash the material with'the water so as tominimize v the amount ofalkali remaining in the material to beneutralized. I next subject the material to an acid treatment, whichdissolves the' chrome and extracts it from the animal fiber. .For thispurpose I use a weak so1ution,say a'one to two per cent. solution, ofsulfuric or sulfurous acids. Pref: erabl-y, wherea light colored productis de-' sired, I use sulfurous acid solution, or a mixtureof sulfurousand sulfuric acids, be-

.cause this, tosome extent, bleaches at the 1 same time that itdissolves out the chrome. After the acid has thoroughly dissolved thechrome, this bath is drained 011:, and inas- 'much as it will containpractically all of the chrome, the latter may be recovered from thedrawn .ofl" liquid by any suitable I process known tochemists. Thematerial is now agam washed to remove excess of acid,

' course, be omitted, since the leather w and then the remaining acidneutralized by a second treatment with weak alkaline solution,preferably lime water, after which the material is washed and thedetanning process thus completed. To make lue or gelatill, the dtannedmaterial will e afterward boiled in the usual manner, while if it is tobe retanned it may be retanned by an ordinary tanning process. s

The detanning process above described results in completely (or at leastto all practical intents) freeing the leather from the tanningchemicals, and this without, so far. as I have been able to determine,in any Wise impairing the tissue structure, strength or origlnalcharacter of the hide materlal. Pieces of leather detanned by the aboveprocess, and then retann'ed, appear to take the second tanning asperfectly and in precisely the same manner as though being tanned forthefirst time.

In the case of detanning freshly tanned h des, for the purpose ofretanning by a different process, for example, the preparatory step ofsoaking up the leather ma of I not be in dry and hard condition.

While I have hereinbefore indicated the preferred chemicals; andindicated these in the proportions which I find best suited to secure te desired results, nevertheless different equivalent chemicals can besubstituted, and the proportions varied within reasonable limits,Without departing from the spirit of the invention.

An important characteristic of the present invention is that throughoutthe entire serles of steps the leather is at no time treated drasticallywith chemical, nor is any step of the treatment continued so long as toresult 1n impairing the tissue structure ofthe ma-' terial.

I claim as my invention:

1.- The improved process of detanning and restoring mineral tannedleather to its original untanned condition, which consists in subjectingthe leather material to treatment in a weak alkaline solutionsubstantiall 1 'free from undissolved mineral matters until the leatheris thoroughly impregnated there: with throlfighout, next substantiallyseparat ing the a aline' solution from the leather and subjecting thelatter to a treatment with an acid having an effective strength, overand above that necessary to neutralize the alkali remaining in thebatch, of not much less than 1% and so weak as to be incapablesubstantially attacking the animal matter during the period that itrequires to completely dissolve the mineral tanning material, andcontinuing this step of the treatment until thetanning chemical has beenthoroughly dissolved, then, before the animal matter has beenappreciably attacked by the chemical, substantially removing the lastmentioned solution.

2. The improved process of detanning and restoring mineral tannedleather to its original untanned condition, which consists in subjectingthe leather material to treatment in a weak. alkaline solutionsubstantially free from undissolved mineral matters until the leather isthoroughly impregnated there with throughout, next substantiallyseparating the alkaline solution from the leather and subjecting thelatter to a treatment with an acid having an effective strength, overand above that necessary to neutralize the alkali remaining in thebatch, of not much less than 1% and so weak asjto be incapable ofsubstantially attackingithe animal matter during the period that itrequires to completely dissolve the mineral tanning material, continuingthis step of the treatment until the tanning chemical has beenthoroughly dissolved, then, before the animal matter has beenappreciably attacked by the chemical, substantially removing the lastmentioned solution,;and subjecting the material to a neutralizingtreatment with a second weak alkaline solution untilit remains alkaline,and finally washing out the free chemicals.

'3. The process of detanning chrome or analogous mineral tanned leatheror leather Waste, which consists in first subjecting the material to ahydrous bath until thoroughly soaked throughout, next subjecting thematerial to a treatment in a bath of lime water substantially free fromsuspended lime, next separating the material from the lime water andsubjecting it to a treatment in an acid solution of a strength notgreater than 10% and not less than1%, next removing the free acidsolution and subjecting the material to treatment with a' neutralizingweak alkaline solution and thereby rendering the batch alkaline, andfinally washing out the free.

chemicals.

T ALBERTGJMANNS.

Witnesses: a ALBERT H. Gmvas,

EMILm Rosa.

